Galactomannans are a class of polysaccharides that are found in the endosperm material of seeds from leguminous plants such as Cyamopsis tetragonoloba (guar gum), Cesalpinia spinosa (tara gum), Ceratonia siliqua (locust bean gum), and other members of the Leguminosae family. A galactomannan is composed of backbone of 1→4-linked β-D-mannopyranosyl main chain units (also designated herein as a mannoside unit or residue) with recurring 1→6-linked α-D-galactosyl side groups (also designated herein as a galactoside unit or residue) branching from the number 6 carbon atom of a mannopyranose residue in the polymer backbone. The galactomannan polymers of the different Leguminosae species differ from one another in the frequency of the occurrence of the galactoside side units branching from the polymannoside backbone. The mannoside and galactoside units are generically referred to herein as glycoside units or residues. The average ratio of D-mannoside to D-galactoside units in the galactomannan contained in guar gum is approximately 1.5 or 2:1, approximately 3:1 for tara gum, and approximately 4:1 for locust bean gum. Another important source of polygalactomannan is isolated from the endosperm of seeds of Cassia tora and Cassia obtusifolia (known as cassia gum). Cassia gum has an average ratio of mannose to galactose of at least 5:1. For illustrative purposes galactomannans obtained from the endosperm of cassia seed can be schematically represented by the structure:
wherein n is an integer representing the number of repeat units in the polymer. The polygalactomannan used in the practice of this invention typically has a weight average molecular weight (Mw) which is within the range of 200,000 to 5,000,000 Daltons. In many cases, the polygalactomannan has a weight average molecular weight, which is within the range of 300,000 to 2,000,000 Daltons. It is common for the galactomannan used in the practice of this invention to have a weight average molecular weight, which is within the range of 400,000 to 1,500,000 Daltons. The molecular weight of the galactomannan can be varied through controlled degradation procedures known in the art.
The underivatized Cassia galactomannan used as a starting material in the practice of this invention typically has a number average molecular weight (Mn) which is within the range of 100,000 to 1,500,000 Daltons. In many cases, the polygalactomannan has a number average molecular weight, which is within the range of 200,000 to 1,000,000 Daltons. In is common for the polygalactomannan used in the practice of this invention to have a number average molecular weight, which is within the range of 300,000 to 800,000 Daltons.
Galactomannans are hydrocolloids that have a high affinity for water. They have been widely used as, thickening, emulsifying, and gelling agents in applications as diverse as foodstuffs, coatings, personal care compositions and in oil well fracturing fluids. Although the use of these polymers has been met with great success, galactomannans used in their natural form have suffered some drawbacks from a water solubility standpoint. An unsubstituted polymannose backbone is completely insoluble in water. The attachment of galactose side units to the C-6 atom in the recurring mannose residues of the polymannose backbone increases the water solubility of the polymer, particularly in cold water (i.e., ambient temperature and below). The greater the galactose side unit substitution, the greater is the cold water solubility properties of the polygalactomannan. Consequently, lower ratios of D-mannosyl to D-galactosyl units in the polygalactomannan leads to better cold water solubility. For example, the polygalactomannan contained in guar gum (average D-mannosyl to D-galactosyl ratio 2:1) is mostly soluble in cold water, while the polygalactomannan obtained from cassia gum (average D-mannosyl to D-galactosyl ratio of at least 5:1) is only sparingly soluble in cold and hot water.
U.S. Pat. No. 4,753,659 to Bayerlein et al. discloses inter alia that improved cold water solubility can be imparted to cassia gum by chemically modifying the polygalactomannan. The reaction of cassia gum polygalactomannan with selected reagents to yield derivatized Cassia is disclosed. Exemplary reaction products include substituted and unsubstituted alkyl ethers, substituted phosphate esters, and substituted quaternary ammonium derivatives. Disclosed uses for the chemically modified cassia gum polygalactomannans include textile printing applications, oil well drilling auxiliaries, mining and explosives applications.
U.S. Pat. No. 7,262,157 to Utz et al. discloses a personal care composition comprising a Cassia galactomannan polymer having repeating units containing a D-mannosyl to D-galactosyl residue ratio of 5 to 1 wherein a portion of the hydrogen groups on the pendant hydroxy substituents on the mannosyl and galactosyl residues are substituted with a group represented by the formula: AR1 wherein A is a substituted or unsubstituted alkylene group containing 1 to 6 carbon atoms, and R1 is a group independently selected from —N+(R3)3X−, —S+(R3)2X−, and —P+(R3)3X−, wherein R3 independently represents substituted and unsubstituted C1-C24 alkyl, substituted and unsubstituted benzyl and substituted and unsubstituted phenyl; and X is any suitable anion that balances the charge on the onium cation.
In personal care, health care, household care, and institutional and industrial care applications the solubility characteristics of active ingredients and formulation aids in aqueous systems are of paramount importance. While the cationically derivatized Cassia galactomannans disclosed in U.S. Pat. No. 7,262,157 are soluble in aqueous based formulations, a relatively high degree of cationic substitution is needed to achieve useful properties. There is a need to provide cationically derivatized Cassia galactomannans that exhibit cationic substantivity across a wide range of substitution levels as well and other properties significant for personal care, health care, household care, and institutional and industrial care applications while retaining significant water solubility. Additionally, there is a need for a cationically and hydrophilically modified galactomannan polymer that imparts significantly better sensory performance in personal care and health care applications. Such galactomannans would have widespread utility in applications not heretofore obtained in the prior art.